The present disclosure relates to an alertness device, a seat equipped with the alertness device, and a method for determining alertness, and particularly to an alertness device having a function to determine alertness, a seat equipped with the alertness device, and a method for determining alertness.
Recently, for stably driving a vehicle, it has been needed to detect a change of a physical condition of a driver. Therefore, various techniques are provided in which various types of parameters indicating conditions of the driver are detect and calculated to thereby determine a change of a physical condition, in particular, alertness of the driver.
For example, Japanese Patent Publication JP4543822B describes that a criterion for determining an occurrence of sleepiness is based on a detection of variations of a depth of respiration, which is periodically repeated at a predetermined number of times, with a focus on the fact that stability of the depth of respiration is lost as a person's condition turns from a state of alertness through a state where conscious sleepiness occurs to an unconscious sleeping state.
Further, PCT Patent Publication WO2010/143535A describes that an average heartbeat, a standard deviation of a respiratory interval of one minute, an value which is obtained by integrating the square of an average heartbeat interval in a case where a predetermined heartbeat interval RRI (R-R Interval) varies to increase and by dividing the integrated value by one minute, and a value which is obtained by averaging a variation ratio in a case where the respiratory interval varies to increase, are set as indicators for determining alertness and that a state of alertness is determined based on the summation of values which are obtained by multiplying these indicators by respective weighting coefficients. As described in PCT Patent Publication WO2010/143535A, in particular, the standard deviation of a respiratory interval of one minute is regarded as an indicator for determining a state of alertness, and such is based on the fact that a person yawns or breathes deeply more often when feeling sleepy and therefore the respiratory interval largely varies compared with a case where the person is sufficiently awake.
In the technique according to Japanese Patent Publication JP4543822B, a respiration signal is disturbed by vibrational noises of a vehicle body; therefore, variations of a depth of respiration are often detected by mistake. Consequently, it is extremely difficult to accurately determine an occurrence of sleepiness. Further, in the technique according to Japanese Patent Publication JP4543822B, a sensor for detecting heartbeats and a sensor for detecting respirations are needed, therefore increasing manufacturing costs. Furthermore, even though variations of respirations at the time of the occurrence of sleepiness are focused on in the alertness determination, in a case where the standard deviation of a respiratory interval is set as the determination indicator, the standard deviation calculated by using a difference between the obtained respiratory interval and an average value of the respiratory interval largely depends on an area where the average value is obtained. In addition, it is difficult to obtain variations of an instantaneous change and the accuracy of the alertness determination is decreased. Thus, it is difficult to appropriately maintain a state of alertness of a person.
Therefore, an alertness device with a high accuracy for determining alertness, a seat equipped with the alertness device, and a method for demining alertness have been desired.